In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Road grading machines include a mounting block that holds one more or rotatable grading tool picks that rotate during operation. The grading picks each have a tip portion that contacts the surface of a road or the ground that is to be milled. To maximize the working life of the tip portion, and thus of the pick, continuous rotational movement of the pick, is essential. Rotation enables the tip portion to be exposed to the road surface from all angles and thus to wear substantially uniformly around its circumference.
FIG. 1 shows a prior art mining pick having fins that surround a head portion of the pick. Mining picks are subjected to very different operating conditions that grading picks. In particular, the material (earth) contacted by mining picks is substantially softer and less abrasive than the material (asphalt, concrete, etc.) contacted by grading picks, such that the forces applied to the tip portion of a mining pick are substantially less than those applied to a grading pick. As a result, the head portion and tip portion of a mining pick have smaller diameters, and the tip portion has less material, than their corresponding parts in a grading pick. Additionally, the softer mining materials are less likely to lodge between the tool pick and the mounting block to prevent rotation of the pick during operation. In the mining pick as shown, a front end of the head portion supports a tip portion. An outer edge of each fin extends frontwardly and radially inwardly from a shoulder located at a rear end of the head portion, the fins terminating near the front end of the head portion. The maximum diameter of the fins is less than or equal to the diameter of the shoulder.
FIGS. 2 and 3 show a prior art grading pick 10. The pick 10 has a front end 12 and a rear end 14. The pick 10 includes a tapered head portion 16, a cutting tip 18 projecting frontwardly from the head portion 16, and a shoulder 20 rearwardly adjacent to the head portion 16 and joining the head portion 16 at a junction 141. A reduced diameter puller groove 22 is disposed rearwardly adjacent to the shoulder 20, and is sized to receive the jaws of a standard extractor tool, as known in the art. Projecting rearwardly form the puller groove 22 is a shank 26 having a diameter sized to be received in a bore in a mounting block (not shown). A tapered portion of the shank 26 immediately adjacent to the puller groove 22 may have a diameter slightly larger than that of the shank 26 to serve as a washer seat 24.
During operation, debris, such as fines, dust, grit, pebbles, dirt, and the like, is produced and can lodge between the grading pick and its mounting block. The debris can become packed and hamper rotation of the pick, and may eventually prevent the pick from rotating entirely, resulting in premature failure of the pick. Conventional picks rely on unbalanced forces between the road surface and the tip portion to cause rotation of the pick within its mounting block, but those unbalanced forces on the tip portion are frequently insufficient to overcome the friction caused by the debris. In such cases, if the lack of rotation of the pick is noticed, an operator may need to manually loosen the grading pick, which is extremely time consuming. But in many cases, either, the lack of rotation goes unnoticed until it is too late, or the operator avoids rotating the pick so the machine can be returned to operation sooner, thereby dramatically shortening the expected life of the pick.
The tip portion of a grading pick is subjected to substantial stresses during operation, and therefore grading picks commonly have a large diameter head portion supporting the tip portion. However, a large diameter head portion demands greater forces than a smaller diameter head portion to achieve the same penetration depth into the road surface.
Accordingly, there is a need in the art for a grading pick that is able to continue to rotate despite the frictional forces imposed by debris generating during operation, and for a grading pick having a smaller diameter head portion to achieve greater penetration into the road surface.